title: Three-dimensional domain swapping and supramolecular protein assembly: insights from the X-ray structure of a dimeric swapped variant of human pancreatic RNase.
abstract: The deletion of five residues in the loop connecting the N-terminal helix to the core of monomeric human pancreatic ribonuclease leads to the formation of an enzymatically active domain-swapped dimer (desHP). The crystal structure of desHP reveals the generation of an intriguing fibril-like aggregate of desHP molecules that extends along the c crystallographic axis. Dimers are formed by three-dimensional domain swapping. Tetramers are formed by the aggregation of swapped dimers with slightly different quaternary structures. The tetramers interact in such a way as to form an infinite rod-like structure that propagates throughout the crystal. The observed supramolecular assembly captured in the crystal predicts that desHP fibrils could form in solution; this has been confirmed by atomic force microscopy. These results provide new evidence that three-dimensional domain swapping can be a mechanism for the formation of elaborate large assemblies in which the protein, apart from the swapping, retains its original fold.
authors.affiliation: Department of Chemical Sciences, University of Naples `Federico II', Via Cintia, 80126 Naples, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Pica
authors.forename: Antonello
authors.initials: A
authors.lastname: Merlino
authors.forename: Alexander K
authors.initials: AK
authors.lastname: Buell
authors.forename: Tuomas P J
authors.initials: TP
authors.lastname: Knowles
authors.forename: Elio
authors.initials: E
authors.lastname: Pizzo
authors.forename: Giuseppe
authors.initials: G
authors.lastname: D'Alessio
authors.forename: Filomena
authors.initials: F
authors.lastname: Sica
authors.forename: Lelio
authors.initials: L
authors.lastname: Mazzarella
mesh_terms: D018360:Crystallography, X-Ray; D005470:Fluorometry; D017353:Gene Deletion; D014644:Genetic Variation; D006801:Humans; D018625:Microscopy, Atomic Force; D011237:Predictive Value of Tests; D015202:Protein Engineering / Q000379:methods*; D017510:Protein Folding; D055503:Protein Multimerization / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D012259:Ribonuclease, Pancreatic / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure
chemical_list: D012259:Ribonuclease, Pancreatic
keywords: atomic force microscopy; fibril formations; ribonuclease; supramolecular aggregates; three-dimensional domain swapping